1. Field of the Invention
The present invention relates to a method for reducing a light intensity of a projection device, in particular for reducing a risk potential to an observer while operating a projection device, in particular a mobile projection device.
2. Description of the Related Art
So-called pico projection devices, also referred to as “projectors” for short or also “beamers,” are known from the related art which are approximately the size of a pack of cigarettes, and which, when connected to a laptop computer, for example, or also as an integral part of an electronic device such as a smart phone, are used for projecting the screen content of the computer or information in general onto a wall surface.
Conventional projectors of this type operate according to the digital light processor (DLP) principle, the liquid crystal on silicon (LCoS) principle, or also as a scanning mirror laser projector. However, the exact mode of operation of these projectors is not discussed in greater detail here.
The conventional projectors share the common feature that the projected visual representation of the information occurs with essentially homogeneous illumination on a projection area. This has the disadvantage, on the one hand, that the available energy of the projector is distributed uniformly over all subareas of the projection area, although often, only one or a few subareas is/are relevant for an observer. This means that for nonrelevant subareas, energy in the form of, for example, light intensity or energy of the projector is unnecessarily consumed, and therefore the time for which the projector, which is generally operated independently of the power grid, i.e., using batteries, for example, is usable is reduced relatively sharply.
On the other hand, the homogeneous illumination of the projection area results in the disadvantage that the luminance of the projected representation may possibly be held at a relatively low total level for energy-saving reasons, resulting in only an unsatisfactory representation for the observer.
Often, the content of only one subarea of the projection area, i.e., approximately 10% to 50% of the total area, is relevant for the observer, at least for a certain period of time, such as for video clips, photo browsers, areas of an application window being processed at the moment for text documents, tables, or drawing programs. In this regard, large-format video presentations or slide shows, which utilize the entire projection area and are carried out using devices which are dependent on the power supply, are not considered, in contrast to the mobile applications discussed here.
In addition, for laser-based devices, due to existing eye safety guidelines the luminous flux emitted by the projector is limited to values which for a full-surface, homogeneously distributed representation likewise allow only unsatisfactory luminance of the projected representation to be achieved. The operation of projection devices which use relatively high-power laser light is perceived as unfavorable, since such laser light may be harmful to health if it strikes a human body, in particular the eyes.